Prior art teachings the disclosures of which go to X-ray film cassettes are U.S. Pat. Nos. 3,703,272; 4,248,172; 4,394,772, and 4,903,288, hereby made of record. Okamato '772 discloses a cassette with a visual check to indicate whether it is loaded or unloaded. McAllister '288 qualifiedly discloses a cassette which when empty is suppose to show a blank indicator, with an X-ray film in it and not exposed is suppose to show a "spot" which indicates presence of film, and with the X-ray film in the cassette in an exposed condition is suppose to show an altered display locked onto the indicator by means of a latching circuit supposed to be energized by reason of a signal from a photocell accepting a light sensor's pulse. However, McAllister '288 does not disclose specific electronic or latching circuits, a means to test whether his device is or is not operational, or optical fiber conduit(s) between sensor and photodiode/electronic circuit.